1. Field of Invention
The present invention relates to a spring device and to a timepiece having this drive device.
2. Description of Related Art
Mechanical timepieces and electronically controlled mechanical timepieces use a mainspring as the drive power source. Assuming the same number of winds, the mechanical energy/volume ratio of a mainspring increases as the maximum output torque increases. The duration time of the mainspring can therefore be increased by either using a spring with greater torque or reducing the torque required to drive the wheel train, but these methods create the need for design changes such as increasing the speed-increasing ratio from the barrel to the second wheel or making the wheel diameters and wheel modules smaller. Both such designs and manufacturing such products are difficult.
As described in Japanese Patent 3582383, we developed a mainspring torque output device that connects the barrel wheel and ratchet wheel using a wheel train with an odd number of wheels. Part of the output torque of the mainspring is returned to the mainspring by speed reducing rotation of the ratchet wheel transferred to the barrel by means of the wheel train, and the spring is wound by the returned torque. The configuration taught in Japanese Patent 3582383 can thus increase the duration time of the mainspring without designing and manufacturing special modules or wheel diameters that are different from usual.
With the configuration taught in Japanese Patent 3582383, however, output power from the mainspring is consumed by winding the spring when the mainspring unwinds and output drops because the barrel wheel and ratchet wheel are connected by a wheel train, and there may not be enough torque to drive the timepiece. This can be resolved by increasing the maximum output torque of the spring, but increasing the volume of the barrel to increase the maximum output of the spring is difficult in small devices such as a timepiece. As a result, further increasing the duration time of the mainspring is difficult with the configuration taught in Japanese Patent 3582383.